Meta: Refactor the way the GUI framework is picked

This is largely based of off the work done by Andrew Kaster in #5918.
Having this toggle makes much more sense, especially if there will be
more UIs in the future.

Co-authored-by: Andrew Kaster <andrew@ladybird.org>

.github/workflows/lagom-template.yml

@@ -173,7 +173,7 @@ jobs:
         if: ${{ inputs.os_name == 'macOS' && inputs.build_preset == 'Sanitizer' }}
         working-directory: ${{ github.workspace }}
         run: |
-          cmake --preset ${{ inputs.build_preset }} -B Build -DENABLE_QT=ON
+          cmake --preset ${{ inputs.build_preset }} -B Build -DLADYBIRD_GUI_FRAMEWORK=Qt
           cmake --build Build
 
       - name: Save Caches

CMakeLists.txt

@@ -53,11 +53,6 @@ endif()
 add_cxx_compile_options(-Wno-expansion-to-defined)
 add_cxx_compile_options(-Wno-user-defined-literals)
 
-if (ANDROID AND ENABLE_QT)
-    message(STATUS "Disabling Qt for Android")
-    set(ENABLE_QT OFF CACHE BOOL "" FORCE)
-endif()
-
 # We need to find OpenSSL in order to link it explicitly with all targets.
 find_package(OpenSSL REQUIRED)
 

Documentation/BuildInstructionsLadybird.md

@@ -254,16 +254,14 @@ Ladybird will be built with one of the following browser frontends, depending on
 * [Qt](https://doc.qt.io/qt-6/) - The UI used on all other platforms.
 * [Android UI](https://developer.android.com/develop/ui) - The native UI on Android.
 
-The Qt UI is available on platforms where it is not the default as well (except on Android). To build the
-Qt UI, install the Qt dependencies for your platform, and enable the Qt UI via CMake:
+The Qt UI is available on platforms where it is not the default as well (except on Android).
+You can pick the UI using the `LADYBIRD_GUI_FRAMEWORK` option, for example to enable the Qt UI:
 
 ```bash
 # From /path/to/ladybird
-cmake --preset default -DENABLE_QT=ON
+cmake --preset default -DLADYBIRD_GUI_FRAMEWORK=Qt
 ```
 
-To re-disable the Qt UI, run the above command with `-DENABLE_QT=OFF`.
-
 ### Build error messages you may encounter
 
 The section lists out some particular error messages you may run into, and explains how to deal with them.

Meta/CMake/gui_framework.cmake

@@ -0,0 +1,17 @@
+if (ANDROID OR VCPKG_TARGET_ANDROID)
+    set(_possible_guis "Android")
+    set(_default_gui "Android")
+elseif (APPLE)
+    set(_possible_guis "AppKit" "Qt")
+    set(_default_gui "AppKit")
+else()
+    set(_possible_guis "Qt")
+    set(_default_gui "Qt")
+endif()
+
+# Note: ladybird_option() doesn't play nicely with this variable, so we use set() directly.
+set(LADYBIRD_GUI_FRAMEWORK ${_default_gui} CACHE STRING "The GUI framework to use for the ladybird application. Possible values: ${_possible_guis}")
+
+if (NOT "${LADYBIRD_GUI_FRAMEWORK}" IN_LIST _possible_guis)
+    message(FATAL_ERROR "Invalid value for LADYBIRD_GUI_FRAMEWORK: ${LADYBIRD_GUI_FRAMEWORK}. Possible values: ${_possible_guis}")
+endif()

Meta/CMake/lagom_options.cmake

@@ -24,9 +24,3 @@ ladybird_option(LAGOM_USE_LINKER "" CACHE STRING "The linker to use (e.g. lld, m
 ladybird_option(LAGOM_LINK_POOL_SIZE "" CACHE STRING "The maximum number of parallel jobs to use for linking")
 ladybird_option(ENABLE_LTO_FOR_RELEASE ${RELEASE_LTO_DEFAULT} CACHE BOOL "Enable link-time optimization for release builds")
 ladybird_option(ENABLE_LAGOM_COVERAGE_COLLECTION OFF CACHE STRING "Enable code coverage instrumentation for lagom binaries in clang")
-
-if (ANDROID OR APPLE)
-    ladybird_option(ENABLE_QT OFF CACHE BOOL "Build ladybird application using Qt GUI")
-else()
-    ladybird_option(ENABLE_QT ON CACHE BOOL "Build ladybird application using Qt GUI")
-endif()

Meta/CMake/presets/CMakeBasePresets.json

@@ -91,7 +91,6 @@
       "cacheVariables": {
         "BUILD_SHARED_LIBS": "OFF",
         "CMAKE_BUILD_TYPE": "RelWithDebInfo",
-        "ENABLE_QT": "OFF",
         "VCPKG_OVERLAY_TRIPLETS": "$env{LADYBIRD_SOURCE_DIR}/Meta/CMake/vcpkg/distribution-triplets",
         "ENABLE_FUZZERS_LIBFUZZER": "ON",
         "ENABLE_ADDRESS_SANITIZER": "ON"

Meta/Lagom/CMakeLists.txt

@@ -50,6 +50,7 @@ endif()
 
 include(check_for_dependencies)
 include(use_linker)
+include(gui_framework)
 include(lagom_options NO_POLICY_SCOPE)
 
 if(ENABLE_ALL_THE_DEBUG_MACROS)

UI/CMakeLists.txt

@@ -47,16 +47,7 @@ function(create_ladybird_bundle target_name)
 endfunction()
 
 # Select UI Framework
-if (ENABLE_QT)
-   add_subdirectory(Qt)
-elseif (APPLE)
-   add_subdirectory(AppKit)
-elseif(ANDROID)
-   add_subdirectory(Android)
-else()
-    # TODO: Check for other GUI frameworks here when we move them in-tree
-    return()
-endif()
+add_subdirectory(${LADYBIRD_GUI_FRAMEWORK})
 
 if (NOT TARGET ladybird)
     message(FATAL_ERROR "UI Framework selection must declare a ladybird target")